1. Field of the Invention
The present invention relates to a supply roller of a developing device for an image forming apparatus, and to a method of manufacturing the supply roller. More particularly, the present invention relates to a supply roller of a developing device for an image forming apparatus, which is small and exhibits excellent toner supply properties while preventing occurrence of a ghost phenomenon and a toner-filming phenomenon which cause a deterioration in the image quality. The invention is further directed to a method of manufacturing the image forming apparatus and the supply roller.
2. Description of the Related Art
In image forming apparatuses, a latent image is formed on a photoreceptor using a light scanner, a toner is supplied from a developing device having toner composition to form an image, and the latent image is developed with toner to form an image. Image forming apparatuses comprise a plurality of rollers, which are necessary to perform various operations. Among these rollers, a supply roller supplies toner from the developing device to the other components such as the photoreceptor.
The general image forming operation in the image forming apparatus is described with reference to FIG. 1 as follows.
FIG. 1 is a view schematically illustrating a standard image forming apparatus.
First, a charging roller 16 charges a photoreceptor 11, and an electrostatic latent image to be developed is formed on the charged photoreceptor 11 by a laser scanning unit (LSU) 18.
A supply roller 13 supplies toner 14 from inside the developing device to a developing roller 12. The toner supplied to the developing roller 12 is thinned to a uniform thickness by a toner layer control apparatus 15, and at the same time is charged due to high friction caused by interaction between the developing roller 12 and the toner layer control apparatus 15.
When the toner passing through the toner layer control apparatus 15 comes into contact with the photoreceptor 11, the latent image formed on the photoreceptor 11 is developed. The developed toner is transferred onto print paper by a transfer roller 19, and then completely fixed onto the print paper so that an image is formed.
If the toner formed on the photoreceptor 11 remains after printing, the toner is cleaned by a cleaning blade 17. The toner separated from the photoreceptor 11 by the cleaning blade 17 is collected separately to be removed later.
The toner in the supply roller 13 in the image forming apparatus has a constant charge to mass ratio (Q/M) in association with the interaction between the developing roller 12 and the toner layer control apparatus 15. The supply roller 13 supplies the toner to the developing roller, and recovers remaining toner not used for the development of the latent image in the developing device.
The supply roller is usually formed from a polyurethane foam or silicone foam. Polyurethane foam has a lower hardness and price than silicone foam.
Recently, image forming apparatuses have been developed with reduced size, longer lifespan, low temperature fixing properties, and a capability of forming glossy images. In particular, color image forming apparatuses have been required to be increasingly miniaturized, because the color image forming apparatuses comprise developing devices containing different color toners.
However, in order to miniaturize the image forming apparatus, each constituent must be miniaturized, but problems arise when miniaturizing the supply roller. When the outer diameter of the supply roller is small, the toner supply properties are reduced and the ghost phenomenon and toner-filming phenomenon occur.
The ghost phenomenon is observed when toner is supplied by a small supply roller to cause unstable electrification of the toner, and as a result, a residual image is formed on the final image unintentionally.
Additionally, the toner-filming phenomenon means that a gap portion of the supply roller is filled with fine toner particles so that the supply roller has inferior supply properties. This problem caused by the toner-filming phenomenon stands out more clearly due to the miniaturization of the supply roller.
Therefore, supply rollers are required which can be manufactured in a small size in response to the need for the miniaturization of image forming apparatuses, and can overcome the above problems caused by miniaturization.